HMC Level Control Question???

[Chris Harding]

Hi Guys

On the HMC series of camera (40,70,80, 150) you can switch your XLR channels to manual BUT you can also switch them to ALC which generally also does a fairly good job.

Now, there is only one "auto/manual" switch so you can either have both XLR's in manual or both in auto!!
In manual you have manual control of each channel BUT what happens when ALC is switched on??

My question is : If you have two mics each on their own XLR channel and one has a much louder sound source than the other... will the ALC circuitry in the camera set ALC levels for each channel independently OR because one source is a lot louder than the other will BOTH channels be pulled down to the level of the highest level mic????

Anybody know how the ALC circuitry is configured and how two uneven sound sources would be set by the camera?????

Chris

[Jonathan Schwartz]

Chris,

It is my understanding that once the XLR adapter is connected to the HMC40, the ALC circuitry is disabled. If you use the mini plug mic input, you can maintain the ALC. I believe I remember that the 150 does not have ALC. I might be wrong about that though.

[Chris Harding]

Hi Jonathan

You are probably right about the HMC40 but my HMC80's have both minijack and XLR (I only use XLR)!! The ALC definately works with XLR inputs as I can switch from front to back. I did a wedding last week as decided to try ALC as the cam was further back from the groom (who had the radio mic) and my Rode mic on the camera levels were pretty low so it seems that the ALC might, in fact, just work on the overall signal input...if there were two circuits (one for each channel) I'm sure it would have tried to pull up the signal level of the on-camera mic...it actually suits me fine that way anyway!!!

Thanks for your input!!!

Chris

[Michael Warren]

Originally Posted by Chris Harding

Anybody know how the ALC circuitry is configured and how two uneven sound sources would be set by the camera?????

Chris,

I don't have an answer for you, but this is how I would test it:

-Connect a constant source to one channel. I'd use a signal generator because I have one, but you could use a tone generated by a computer or even place a mic next to a speaker on a music player.

-Connect a mic to the other channel and, while recording, tap it with your hand. The ALC will see the pulse from your hand as an overload and turn the level down.

Playback the audio (or look at the waveform) and see if the constant channel was reduced when you overloaded the other one. There may be a small amount of bleed, but you should still be able to easily tell.

That said, I would expect there to be an independent ALC for each channel since the camera is designed to have 2 independent sources connected to the XLRs.

[Chris Harding]

Hey Michael

Nice to see another Aussie here!!!

I have just done that test and you are correct..the ALC circuits are independent from each other!! With a constant source in one mic and varying the source dramatically in the other makes no difference to the first channel at all. This is because I had a radio mic in the room next door next to the clock radio and the cam was in my office and I just yelled into the mic now and again so it went to a high level from an ambient level.

Because I had a physical barrier there was no problem BUT at a wedding where I have two radio mics and an on camera mic with all three being able to pick up the same source (the priest has a PA too!!!) you start having physical issues.

Thanks I'm happy now..in fact I used ALC on two weddings last week and no issue at all!!!

Chris

[Michael Warren]

Originally Posted by Chris Harding

Nice to see another Aussie here!!!

I've been lurking for several years. :)

I just yelled into the mic now and again

I bet your neighbours were wondering what was going on. :)

in fact I used ALC on two weddings last week and no issue at all!!!

Good to hear. I haven't shot a wedding for over 16 years. Sound was always the biggest hassle to get right.